This invention relates to a magnetic medium, such as a thin film magnetic recording medium, and the method of manufacturing the medium. The invention has particular applicability to a magnetic recording medium exhibiting low noise, high coercivity and suitable for high-density longitudinal and perpendicular recording.
The requirements for high areal density impose increasingly greater requirements on magnetic recording media in terms of coercivity, remanent squareness, low medium noise and narrow track recording performance. It is extremely difficult to produce a magnetic recording medium satisfying such demanding requirements, particularly a high-density magnetic rigid disk medium for longitudinal and perpendicular recording. The magnetic anisotropy of longitudinal and perpendicular recording media makes the easily magnetized direction (the easy axis of magnetization) of the media located in the film plane and perpendicular to the film plane, respectively. The remanent magnetic moment of the magnetic media after magnetic recording or writing of longitudinal and perpendicular media is located in the film plane and perpendicular to the film plane, respectively.
To accommodate for increased areal density, design of magnetic media is one of the key factors. The main limitation in media is the so-called xe2x80x9csuperparamagneticxe2x80x9d effect, which can be interpreted simply as follows: to achieve high areal density media, the grain size of the magnetic film needs to be reduced. However, when grain size approaches 100 xc3x85, the energy needed to switch the easy axis of magnetization of one grain to that of the other becomes smaller than the thermal energy if the grains are weakly coupled. That is, the thermal energy destroys the magnetism by randomizing the magnetization of the small grains, and the grains can not hold permanent magnetization any more. Therefore, it has become extremely important to make xe2x80x9cthermally stablexe2x80x9d magnetic films with grains smaller than 100 xc3x85 for high areal density applications.
A substrate material conventionally employed in producing magnetic recording rigid disks comprises an aluminum-magnesium (Alxe2x80x94Mg) alloy. Such Alxe2x80x94Mg alloys are typically electrolessly plated with a layer of NiP at a thickness of about 15 microns to increase the hardness of the substrates, thereby providing a suitable surface for polishing to provide the requisite surface roughness or texture.
Other substrate materials have been employed, such as glass, e.g., an amorphous glass, glass-ceramic material which comprise a mixture of amorphous and crystalline materials, and ceramic materials. Glass-ceramic materials do not normally exhibit a crystalline surface. Glasses and glass-ceramics generally exhibit high resistance to shocks.
A conventional longitudinal recording disk medium is depicted in FIG. 1 and typically comprises a non-magnetic substrate 10 having sequentially deposited on each side thereof an underlayer 11, 11xe2x80x2, such as chromium (Cr) or Cr-alloy, a magnetic layer 12, 12xe2x80x2, typically comprising a cobalt (Co)-base alloy, and a protective overcoat 13, 13xe2x80x2, typically containing carbon. Conventional practices also comprise bonding a lubricant topcoat (not shown) to the protective overcoat. Underlayer 11, 11xe2x80x2, magnetic layer 12, 12xe2x80x2, and protective overcoat 13, 13xe2x80x2, are typically deposited by sputtering techniques. The Co-base alloy magnetic layer deposited by conventional techniques normally comprises polycrystallites epitaxially grown on the polycrystal Cr or Cr-alloy underlayer. A conventional perpendicular recording disk medium is similar to the longitudinal recording medium depicted in FIG. 1, but does not comprise Cr-containing underlayers.
Conventional methods for manufacturing longitudinal magnetic recording medium with a glass or glass-ceramic substrate comprise applying a seed layer between the substrate and underlayer. A conventional seed layer seeds the nucleation of a particular crystallographic texture of the underlayer.
Conventional Cr-alloy underlayers comprise vanadium (V), titanium (Ti), tungsten (W) or molybdenum (Mo). Other conventional magnetic layers are CoCrTa, CoCrPtB, CoCrPt, CoCrPtTaNb and CoNiCr.
A conventional longitudinal recording disk medium is prepared by depositing multiple layers of metal films to make a composite film. In sequential order, the multiple layer typically comprise a non-magnetic substrate, one or more underlayers, a magnetic layer, and a protective carbon layer. Generally, a polycrystalline epitaxially grown cobalt-chromium (CoCr) magnetic layer is deposited on a chromium or chromium-alloy underlayer.
The seed layer, underlayer, and magnetic layer are conventionally sequentially sputter deposited on the substrate in an inert gas atmosphere, such as an atmosphere of pure argon. A conventional carbon overcoat is typically deposited in argon with nitrogen, hydrogen or ethylene. Conventional lubricant topcoats are typically about 20 xc3x85 thick.
The linear recording density could be increased by increasing the coercivity of the magnetic recording medium. However, this objective could only be accomplished by decreasing the medium noise, as by maintaining very fine magnetically noncoupled grains. As the recording areal density increases, conventional magnetoresistive (MR) disks have smaller grain size, which induces superparamagnetic limit and causes the collapse of medium coercivity and magnetic remanance. Also, conventional sputtered media rely on the magnetic alloy composition to increase volume anisotropy.
There exists a need for technology enabling the use of a structure that make xe2x80x9cthermally stablexe2x80x9d magnetic films with grains smaller than 100 xc3x85 for high areal density applications.
During the course of the present invention, it was found that modifying the substrate plating composition so that during sputtering, special film, such as oxide film, with uniform and extremely fine grains ( less than 100 xc3x85) can form on the top of the substrate surface. The subsequent growth of magnetic films will be pre-defined by the special oxide film. Uniform grains ( less than 100 xc3x85) of magnetic film could be formed on top of the oxide grains underneath, with narrow grain size distribution. Because of the narrow grain size distribution, one could eliminate magnetic grains which are too small to be thermally stable while maintaining the small mean grain size for good signal-to-noise performance. As a result, the xe2x80x9csuperparamagneticxe2x80x9d effect will be pushed further down to higher areal densities.
An embodiment of this invention is a magnetic recording medium, comprising a substrate, a Nixe2x80x94Pxe2x80x94X containing layer on the substrate and a magnetic layer with segregated Co-containing grains on the Nixe2x80x94Pxe2x80x94X containing layer, wherein X has a higher oxidation potential than that of Ni and X is not W. In other embodiments, X is selected from the group consisting of Al, Co, Cr, Fe, Ti, V, Cd, Zr, Mn and Mo. The magnetic recording medium could further comprise an underlayer comprising at least one layer of Cr or Cr-based alloy on the Nixe2x80x94Pxe2x80x94X containing layer and an optional intermediate layer comprising a CoCr-based alloy on the underlayer. The segregated Co-containing grains have a mean grain diameter of about 100 xc3x85 or less. The mean grain diameter could be measured by performing a grain size analysis of transmission electron microphotographs of the magnetic layer. The magnetic recording medium could comprise an oxide layer in between the Nixe2x80x94Pxe2x80x94X containing layer and the magnetic layer. The oxide layer could comprise additive-rich-oxide grains and Ni-rich oxide grains. The additive-rich-oxide grains could have a spacing between adjacent additive-rich-oxide grains of about 100 xc3x85 or less. The oxide layer could have a thickness of about 5 to 100 xc3x85. The magnetic layer could have a thickness of about 100 to 300 xc3x85. The substrate could be a glass substrate or an aluminum substrate, the underlayer could be CrW, CrV, CrTi or CrTa and the intermediate layer could be CoCr, CoCrPt, CoCrPtTa or CoCrPtB.
Another embodiment of this invention is a method of manufacturing a magnetic recording medium, the method comprising depositing a Nixe2x80x94Pxe2x80x94X containing layer on a substrate and depositing a magnetic layer on the Nixe2x80x94Pxe2x80x94X containing layer, wherein X has a higher oxidation potential than that of Ni and X is not W.
The method could further comprise depositing an oxide layer on the Nixe2x80x94Pxe2x80x94X containing layer, depositing an underlayer comprising at least one layer of Cr or Cr-based alloy on the oxide layer and depositing an optional intermediate layer comprising a CoCr-based alloy on the underlayer.
Another embodiment is a magnetic recording medium, comprising a substrate; a magnetic layer comprising segregated Co-containing grains and means for nucleating the segregated Co-containing grains of the magnetic layer on the substrate. The means for nucleating the segregated Co-containing grains could be the substrate or a film on the substrate, wherein the substrate and/or the film contains nucleation sites for the nucleation and growth of the segregated Co-containing grains of the magnetic layer. Preferably, the magnetic layer would inherit the structure of the film underneath containing the nucleation sites.
Additional advantages and other features of the present invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the present invention. The drawings and description are to be regarded as illustrative in nature, and not as restrictive.